getaddrinfo(3)             Linux Programmer's Manual            getaddrinfo(3)

       getaddrinfo - network address and service translation

       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>

       int getaddrinfo(const char *node, const char *service,
                       const struct addrinfo *hints,
                       struct addrinfo **res);

       void freeaddrinfo(struct addrinfo *res);

       const char *gai_strerror(int errcode);

       The  getaddrinfo(3) function combines the functionality provided by the
       getipnodebyname(3),  getipnodebyaddr(3),  getservbyname(3),  and   get-
       servbyport(3)  functions  into  a  single  interface.   The thread-safe
       getaddrinfo(3) function creates one or more socket  address  structures
       that can be used by the bind(2) and connect(2) system calls to create a
       client or a server socket.

       The getaddrinfo(3) function is not  limited  to  creating  IPv4  socket
       address  structures;  IPv6  socket address structures can be created if
       IPv6 support is available.  These socket address structures can be used
       directly  by  bind(2)  or  connect(2),  to prepare a client or a server

       The addrinfo structure used by this  function  contains  the  following

       struct addrinfo {
           int     ai_flags;
           int     ai_family;
           int     ai_socktype;
           int     ai_protocol;
           size_t  ai_addrlen;
           struct sockaddr *ai_addr;
           char   *ai_canonname;
           struct addrinfo *ai_next;

       getaddrinfo(3)  sets  res to point to a dynamically-allocated link list
       of addrinfo structures, linked by the ai_next member.  There  are  sev-
       eral  reasons  why the link list may have more than one addrinfo struc-
       ture, including: if the network host is multi-homed;  or  if  the  same
       service  is  available  from multiple socket protocols (one SOCK_STREAM
       address and another SOCK_DGRAM address, for example).

       The members ai_family, ai_socktype, and ai_protocol have the same mean-
       ing  as the corresponding parameters in the socket(2) system call.  The
       getaddrinfo(3) function returns socket addresses in either IPv4 or IPv6
       address  family, (ai_family will be set to either PF_INET or PF_INET6).

       The hints parameter specifies the preferred socket type,  or  protocol.
       A  NULL hints specifies that any network address or protocol is accept-
       able.  If this parameter is not NULL it points to an addrinfo structure
       whose  ai_family, ai_socktype, and ai_protocol members specify the pre-
       ferred socket type.  PF_UNSPEC in ai_family specifies any protocol fam-
       ily   (either  IPv4  or  IPv6,  for  example).   0  in  ai_socktype  or
       ai_protocol specifies that any socket type or protocol is acceptable as
       well.  The ai_flags member specifies additional options, defined below.
       Multiple flags are specified by logically OR-ing  them  together.   All
       the  other  members  in the hints parameter must contain either 0, or a
       null pointer.

       The node or service parameter, but not both, may be NULL.  node  speci-
       fies  either  a  numerical  network  address (dotted-decimal format for
       IPv4, hexadecimal format for IPv6) or a network hostname, whose network
       addresses  are  looked  up and resolved.  If the ai_flags member in the
       hints parameter contains the AI_NUMERICHOST flag then the node  parame-
       ter  must be a numerical network address.  The AI_NUMERICHOST flag sup-
       presses any potentially lengthy network host address lookups.

       The getaddrinfo(3) function creates a link list of addrinfo structures,
       one for each network address subject to any restrictions imposed by the
       hints parameter.  ai_canonname is set to point to the official name  of
       the host, if ai_flags in hints includes the AI_CANONNAME flag.  ai_fam-
       ily, ai_socktype, and ai_protocol specify the socket  creation  parame-
       ters.  A pointer to the socket address is placed in the ai_addr member,
       and the length of the socket  address,  in  bytes,  is  placed  in  the
       ai_addrlen member.

       If  node  is NULL, the network address in each socket structure is ini-
       tialized according to the AI_PASSIVE flag, which is set in the ai_flags
       member  of  the  hints  parameter.   The network address in each socket
       structure will be left unspecified if AI_PASSIVE flag is set.  This  is
       used  by server applications, which intend to accept client connections
       on any network address.  The network address will be set to  the  loop-
       back interface address if the AI_PASSIVE flag is not set.  This is used
       by client applications, which intend to connect to a server running  on
       the same network host.

       service  sets  the  port  number  in the network address of each socket
       structure.  If service is NULL the port number will be left  uninitial-

       The  freeaddrinfo(3)  function  frees the memory that was allocated for
       the dynamically allocated link list res.

       getaddrinfo(3) returns 0 if it succeeds, or one of the  following  non-
       zero error codes:

              The requested address family is not supported at all.

              The requested socket type is not supported at all.

              ai_flags contains invalid flags.

              The  node  or service is not known.  This error is also returned
              if both node and service are NULL.

              The requested service is not available for the requested  socket
              type.  It may be available through another socket type.

              The  specified  network host does not have any network addresses
              in the requested address family.

              The specified network host exists, but does not have any network
              addresses defined.

              Out of memory.

              The name server returned a permanent failure indication.

              The  name  server  returned a temporary failure indication.  Try
              again later.

              Other system error, check errno for details.

       The gai_strerror(3) function translates these error codes  to  a  human
       readable string, suitable for error reporting.

       getipnodebyname(3), getipnodebyaddr(3)

Linux Man Page                    2000-12-18                    getaddrinfo(3)